Comparison between thermophysical and tribological properties of two engine lubricant additives: electrochemically exfoliated graphene and molybdenum disulfide nanoplatelets

Abstract

Recently graphene and other 2D materials were suggested as nano additives to enhance the performance of nanolubricants and reducing friction and wear-related failures in moving mechanical parts. Nevertheless, up to our knowledge there are not previous studies on electrochemical exfoliated nanomaterials as lubricant additives. In this work, engine oil-based nanolubricants were developed via two-steps method using two different 2D nanomaterials: a carbon-based nano additive, graphene nanoplatelets (GNP) and a sulphide nanomaterial, molybdenum disulfide (MoS 2 ) nanoplatelets (MSNP). The influence of these nano additives on the thermophysical properties of the nanolubricants, such as viscosity index, density and wettability, was investigated. The unique features of the electrochemical exfoliated GNP and MSNP allow the formulation of nanolubricant with unusual thermophysical properties. Both the viscosity and density of the nanolubricants decreased by increasing the nanoplatelets loading. The effect of the nano additives loading and temperature on the tribological properties of nanolubricants was investigated using two different test configurations: reciprocating ball-on-plate and rotational ball-on-three-pins. The tribological specimens were analysed by Scanning Electron Microscopy (SEM) and 3D profiler in order to evaluate the wear. The results showed significant improvement in the antifriction and anti-wear properties, for the 2Dmaterials-based nanolubricants as compared with the engine oil, using different contact conditions. For the reciprocal friction tests, maximum friction and worn area reductions of 20% and 22% were achieved for the concentrations of 0.10 wt% and 0.20 wt% GNP, respectively. Besides, the best anti-wear performance was found for the nanolubricant containing 0.05 wt% MSNP in rotational configuration test, with reductions of 42% and 60% in the scar width and depth, respectively, with respect to the engine oil.

Surface Modification of Transition Metal Dichalcogenide Nanosheets for Intrinsically Self‐Healing Hydrogels with Enhanced Mechanical Properties

“…[13] Furthermore, 2D TMDs like MoS 2 and WS 2 have experimentally proven to show exceptional tribological performance (even better than graphene). [14,15] They are of key importance as a solid lubricant or as a lubricant additive to the industry. Therefore, it would be ideal to introduce hydrogen bonding sites on TMDs to make mechanically robust and selfhealable polymer nanocomposites for next-generation applications such as self-lubricating surfaces or flexible electronics.…”

Thermophysical and Tribological Properties of Highly Viscous Biolubricants

“…The contact angle, θ, of the two formulated biodegradable oils on steel surfaces was measured using the sessile drop method through a contact angle analyzer, Phoenix MT­(A), at 303.15, 323.15, and 353.15 K. Figure shows the experimental procedure used for the contact angle measurements. The experimental setup was further described previously. , The same surface material of the disks used for the tribological tests was also selected to evaluate the wettability behavior (chrome steel disks AISI 52100). The surface was rinsed with ethanol and dried with a stream of hot air, before each measurement.…”

Additivation of MoS2 nanosheets to synthetic poly-alpha-olefins base oils: A theoretical study of nanolubrication

“…The use of Trivalent Metal Dichalcogenides (TMDs), especially MoS 2 , as nanoadditives for base lubricant oils has been considered in the literature [3,4]. Many different geometries for TMDs nanoadditives have been proposed starting from nanosheets (hydrothermally synthesized [5] or electrochemically exfoliated [6]) to complex structures like flower-like [7] or spherical nanoparticles [8], and advanced structures like nano-MoS 2 quantum dots [9]. MoS 2 nanoparticles have proved to reduce friction and wear in concentrations below 2 wt% for different types of base oils [10].…”